Rave valve theory question

[Bonmotwang]

I've actually already tried that. The bushing was even taller than the base, but I believe the end result was the same: broken rave piston. It's been a long time, but I remember that in the end, it wasn't noticeably better than it was. Also, finding an exact match for a bushing is very hard. I found some on grainger.com but they turned out to not be true "tubes", but rather a flat peice of metal folded. There was a seam where it came together. Perhaps this allowed the extra gasses by.

That's why I am thinking this is not about the hot gas going into the bellow that melts the piston.
Otherwise every time piston melts, the rubber bellow would be overheated or melt.

If the melting point is at the thread, it tells us the heat source is not the hot exhaust gas in the bellow, but the hot exhaust gas around the guillotine at the bottom.

 

[IDoSeaDoo]

You're saying that the heat travels up the shaft of the Rave valve and melts the plastic? That could be.... Perhaps there is a lean condition occurring at some point of the power band, say in the lower RPMs. Maybe this is when it's overheating. The valve would be receiving a lot more exposure to the exhaust stream as it would be in the down position. This ski has suffered from a hesitation for years now when you accelerate from idle, so perhaps this is causing heat spikes? I have not been able to fix this 100% and have just been dealing with it... Could this be the root cause of the problem??

 

[Bonmotwang]

You're saying that the heat travels up the shaft of the Rave valve and melts the plastic? That could be.... Perhaps there is a lean condition occurring at some point of the power band, say in the lower RPMs. Maybe this is when it's overheating. The valve would be receiving a lot more exposure to the exhaust stream as it would be in the down position. This ski has suffered from a hesitation for years now when you accelerate from idle, so perhaps this is causing heat spikes? I have not been able to fix this 100% and have just been dealing with it... Could this be the root cause of the problem??

I am only a humble logical thinker and only guessing from what I have learned from this forum and my two water crafts.

Yes, the shaft transfer heat very fast with a wide end (guillotine ) to collect heat from.
Is it aluminum? which is the material used on heat sinks. So you don't see too much of differential temperature between the big end and the thread.
The plastic melts (there no really "melting point" for plastic) between 130C and 160C depends on different types.
So a momentary heat spike (30 - 60 seconds? not sure) may be enough to soften the plastic.

 

[Sportster-2001-951C-Stock]

I can see if the plastic used to make the piston is the wrong type (too brittle) then they might crack or break as well. This kind of situation is where we get into trouble by thinking aftermarket parts made in China by someone who's only in it to make a buck are acceptable replacements. Meanwhile the guys making good parts get squeezed.

I like the aluminum piston idea at this point, tightening the garter spring might address the problem of the groove not being machined deep enough, or some bellows adhesive might also be able to help in that case as well.

It'll be interesting to see your results.

 

[Bonmotwang]

Another idea: drill some went holes on the black cup to help dissipating the heat?


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[IDoSeaDoo]

Well, turns out that the website from which I "bought" those rave pistons is actually out of stock. The site malfunctioned and let me buy them anyway. Doesn't appear to be any anywhere. I'll be contacting their supplier on tuesday to see if there are any on the West coast. Otherwise, it's time to build a foundry and cast some

 

[Bonmotwang]

Well, turns out that the website from which I "bought" those rave pistons is actually out of stock. The site malfunctioned and let me buy them anyway. Doesn't appear to be any anywhere. I'll be contacting their supplier on tuesday to see if there are any on the West coast. Otherwise, it's time to build a foundry and cast some

CNC will be a lot faster


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[IDoSeaDoo]

Probably, but the closest thing I have to CNC equipment is a drill and a dremel LOL. It also looks like I won't be getting to this any time soon. The 787 just took another crap yesterday. Sounds like I lost another crank, this one being maybe 30 hours old. Can't wait to pull the head and see. I'll be sure to track down who I got it from and let you guys know if it really was the crank.

I seem to have the worst luck with 787s I wish there was an alternative to the X4, but nothing fits the ticket of small, light, fast and good-looking... I would put a 951 in there, but I hear they're just as unreliable as the 787s. Thoughts?

 

[LouDoo]

Probably, but the closest thing I have to CNC equipment is a drill and a dremel LOL. It also looks like I won't be getting to this any time soon. The 787 just took another crap yesterday. Sounds like I lost another crank, this one being maybe 30 hours old. Can't wait to pull the head and see. I'll be sure to track down who I got it from and let you guys know if it really was the crank.

I seem to have the worst luck with 787s I wish there was an alternative to the X4, but nothing fits the ticket of small, light, fast and good-looking... I would put a 951 in there, but I hear they're just as unreliable as the 787s. Thoughts?

A 95XP 717, X4 hull, fast, light weight, probably the most trouble free ski I ever owned. No RAVE valves.

Lou

 

[Bonmotwang]

A 95XP 717, X4 hull, fast, light weight, probably the most trouble free ski I ever owned. No RAVE valves.

Lou

Is the biggest design difference between 717 and 787 the rave beside the displacement?



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[Bonmotwang]

Probably, but the closest thing I have to CNC equipment is a drill and a dremel LOL.

If Anyone has a cad drawing or 3d model, I can get it around in 4 weeks for a pair for someone to play with.


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[1983]

Andrew, its Rob from Raleigh. What happened at lake yesterday? What are the symptoms?

If you need a motor to use as rebuild I am selling this setup as parts or whole: http://www.seadooforum.com/showthread.php?74645-Parting-or-Selling-Complete-95-XP800 Just an option for you that is local so you don't have to mess with shipping. I also have that complete 96' 787 GSX setup for sale if you need parts lemme know.

That would be sweet if someone could enter the rave assembly into a CAD program. I messed with 3D studiomax, autocad and whatnot in highschool but technology has changed vastly since then. Then [MENTION=68537]Bonmotwang[/MENTION] could have it cut.

Rob

Probably, but the closest thing I have to CNC equipment is a drill and a dremel LOL. It also looks like I won't be getting to this any time soon. The 787 just took another crap yesterday. Sounds like I lost another crank, this one being maybe 30 hours old. Can't wait to pull the head and see. I'll be sure to track down who I got it from and let you guys know if it really was the crank.

I seem to have the worst luck with 787s I wish there was an alternative to the X4, but nothing fits the ticket of small, light, fast and good-looking... I would put a 951 in there, but I hear they're just as unreliable as the 787s. Thoughts?

 

[Bonmotwang]

Also the cone. If anybody has it modelled. I can take it over from there and design a better way for the oil plug.


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[Sportster-2001-951C-Stock]

A 95XP 717, X4 hull, fast, light weight, probably the most trouble free ski I ever owned. No RAVE valves.

Lou

I think that might be the one I had, no balance shaft, right? Dunno if it was X4 but that thing ran and ran, like a top. Not a ski for speed demons but was plenty fast for me, rode less than half throttle most of time and it would get out of the water fast.

What a great ski that thing was!

 

[Sportster-2001-951C-Stock]

I would put a 951 in there, but I hear they're just as unreliable as the 787s. Thoughts?

Everybody says the 787 is more reliable than the 951 and I have to think it should be. If there's anything I wonder about concerning the 787, it's the PTO balance shaft bearing.

 

[Bonmotwang]

Everybody says the 787 is more reliable than the 951 and I have to think it should be. If there's anything I wonder about concerning the 787, it's the PTO balance shaft bearing.

Does this bearing get lubricated by the oil put in through that big oil plug hole?


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[Sportster-2001-951C-Stock]

Does this bearing get lubricated by the oil put in through that big oil plug hole?


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I'm pretty sure the bearing itself is sealed with grease inside but that end of the balance shaft (drive end) is not sealed completely from the PTO crankcase so the original oil is eventually "replaced" by 2-stroke oil.

I guess it works fine that way, but it's possible if the crankcase becomes water flooded the water becomes trapped in that area of the bearing and CB drive gear. Supposedly after some time running (an hour or two?) the water eventually is evaporated or in some cases can be evacuated or drained and refilled using 30wt oil.

seadoosource has a page on changing 951/787 CB oil and explains this fairly well for the 787.

 

[Bonmotwang]

I'm pretty sure the bearing itself is sealed with grease inside but that end of the balance shaft (drive end) is not sealed completely from the PTO crankcase so the original oil is eventually "replaced" by 2-stroke oil.

I guess it works fine that way, but it's possible if the crankcase becomes water flooded the water becomes trapped in that area of the bearing and CB drive gear. Supposedly after some time running (an hour or two?) the water eventually is evaporated or in some cases can be evacuated or drained and refilled using 30wt oil.

seadoosource has a page on changing 951/787 CB oil and explains this fairly well for the 787.

Adding oil into the CB oil plug becomes a maintenance routine then. A few times per season?
Back to the bearing, is there a way to "maintain" it?


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[LouDoo]

The counterbalance cavity on 787's and 951's don't usually require service, the manual states only if the engine has been submerged. It's a sealed cavity and normally only filled with oil when the engine is new or when the engine is rebuilt. Early 787's, 95, 96 and some 97's are not even serviceable.

This thread is off the original topic, Rave valves, so lets get back to the original topic.

Lou

 

[IDoSeaDoo]

Andrew, its Rob from Raleigh. What happened at lake yesterday? What are the symptoms?

If you need a motor to use as rebuild I am selling this setup as parts or whole: http://www.seadooforum.com/showthread.php?74645-Parting-or-Selling-Complete-95-XP800 Just an option for you that is local so you don't have to mess with shipping. I also have that complete 96' 787 GSX setup for sale if you need parts lemme know.

That would be sweet if someone could enter the rave assembly into a CAD program. I messed with 3D studiomax, autocad and whatnot in highschool but technology has changed vastly since then. Then [MENTION=68537]Bonmotwang[/MENTION] could have it cut.

Rob

Thanks for the offer Rob, but I have plenty of cases and stuff myself. I tore it apart, and at first thought I maybe ate a rave or something. But I ripped the head off and found that I lost the crank. The same one I replaced with a rebuilt one just a year ago. It MAYBE had 30 hours on it! I have another from the same rebuilder, but am now skeptical. It gave out with absolutely no warning. One second I'm doing bunny-hops, the next I'm dead in the water. :facepalm: Good thing Suke was there to tow me in. I think I lost it bad this time. Like snapped a rod or something. One piston doesn't move at all and is just stuck down at the bottom. I did notice something very ominous though, and something everyone here should check right away: my drain line that runs from the back of the jugs to the exhaust outlet was totally blocked with sand. That's why my jugs always seemed to run a bit hot. It never set off the beeper, but I'm sure it affected cooling none the less. Everyone, go check this on your ski right away. No amount of flushing will clear such a block.

 

[bobseider]

How to get a stuck head off a motor?

Does yours have items 15, 16, 17 inside as the 951 does, I don't see them in the drawing referenced above?

do you have any secerts to getting a stuck head off of a 951?

 

[Sportster-2001-951C-Stock]

Does yours have items 15, 16, 17 inside as the 951 does, I don't see them in the drawing referenced above?

do you have any secerts to getting a stuck head off of a 951?

Hi Bob, I guess your cylinder head is stuck and you are trying to remove it. You will need a new replacement head gasket, FWIW.

So to your question, I guess there may be some corrosion around the stud bolts perhaps, especially if it has been used in saltwater, and this can make it very difficult to remove the head.

It may be necessary to damage the head by chiseling or cutting it away or possibly the studs by using a stud extractor on the exposed threaded portion but first make sure all of the head bolts are removed and try a 50/50 mixture of automatic transmission fluid and acetone solvent around all the head bolts/studs to loosen the aluminum chloride/oxide corrosion.

50/50 mixture of acetone and automatic transmission fluid soaking for a few days keep applying and smack the head studs with a dead-blow plastic hammer or wooden block (avoid damaging the threaded studs by impact on threads) can penetrate as well as any penetrating fluid aside perhaps a product called Kriol, but personally I think the ATF/Acetone mix is just as good.

Also, I often use compressed air to lift a head by rolling the piston to top of cylinder and applying compressed air through the spark plug hole. Perhaps you have a cylinder compression gauge connection hose you can use to connect to an air compressor ans help to push the head off.

A third way to help coax the head off a 2-stroke (careful trying this with a 4-stroke, can bend the valves if they're not closed) is by threading a few feet of rope into the cylinder through the spark plug hole so the combustion chamber is full of rope and then turn the crankshaft back and forth to dislodge the cylinder head from the force of the piston upward against the rope. Try not to get the rope caught in one of the cylinder exhaust ports, so pay close attention for this possibility.

Good luck with your 951!